RedHat was never worried about CentOS, the people/companies using CentOS never had the budgets for RedHat anyway and the companies using RedHat often need certification and support contracts (due to regulations). So CentOS never was seen as a competition I would argue.

However, once Oracle started "repackaging" RedHat, and making indents RedHat acted quickly and essentially made using their patches much more difficult (https://www.zdnet.com/article/red-hat-turns-on-oracle-and-ot...).